A mold used for vacuum molding capable of bringing a cavity into a vacuum state after the mold is clamped is known as a conventional one.
Patent Document 1: Japanese Published Unexamined Patent Application No. 2002-225096
Patent Document 2: Japanese Published Unexamined Patent Application No. 2001-129833
A mold disclosed by Patent Document 1 (2002-225096) or Patent Document 2 (2001-129833) is composed of a stationary mold half and a movable mold half. An annular groove is formed in a parting surface of one of the stationary and movable mold halves. An O-ring is disposed in the groove.
When the stationary mold half and the movable mold half are clamped together, the O-ring comes into elastic contact with the parting surface of one of the mold halves, so that a cavity formed inside the groove can be kept in a state of being sealed off from the outside. Under this state, a vacuum pump communicating with the cavity is operated, and, as a result, the cavity can create a vacuum.
For example, the mold disclosed by Patent Document 1 (2002-225096) has a vent, which is an opening used for vacuuming, formed in a contact surface between the stationary mold half and the movable mold half. The vent is opened toward a cavity formed by the stationary and movable mold halves, and leads to a vacuum apparatus through an exhaust passage bored in the movable mold half. The thus structured mold can keep the cavity in a vacuum state by being clamped and then allowing the vacuum apparatus to evacuate air from the cavity through the vent and the exhaust passage.
However, a conventional problem resides in the fact that, since the mold uses the O-ring by which the cavity is sealed off, the O-ring is broken or reduced in elasticity by repeatedly performing a molding operation, and hence a drop in sealability makes it impossible to maintain the sealed state. Another conventional problem is that, since the mold has the O-ring sandwiched between the stationary mold half and the movable mold half when clamped, there is a need to, for example, adjust a clamping pressure when clamped, and hence much time is consumed for molding, and restrictions are imposed on the molding operation.
Additionally, since the mold disclosed by Patent Document 1 (2002-225096) has the vent opened toward the cavity, there has been a fear that molten resin will enter the vent when the molten resin is injected into the cavity. Still additionally, disadvantageously, a molded article has a part formed by the vent that needs to be processed, thereby increasing man-hours.
The present invention has been made in consideration of these problems. It is therefore an object of the present invention to provide an injection mold capable of maintaining sealability even if a molding operation is repeatedly performed, and provide a method of manufacturing the mold. It is another object of the present invention to provide an injection mold capable of reliably keeping a cavity in a vacuum state and capable of producing molded articles at low cost without creating extra work for the molded articles after completing the molding operation, an injection molding apparatus, and an injection molding method.